A devastating tornado tore through Moore, Oklahoma on Monday,killing at least 24 and leaving the city looking like “a debrisfield,” according to comments Mayor Glenn Lewis made to NBC.

The tornado was one of at least 22 tornadoes that struck acrosssix states on Monday, a day after a northeast-moving storm spawnedover 20 tornadoes through Texas, Minnesota, Kansas, Illinois, Iowa,Missouri, Nebraska and Oklahoma.

The Insurance Information Institute says it will take weeks tocalculate the number of insured losses and claims resulting fromyesterday's natural disaster, but I.I.I. adds that tornadoes thisspring have been some of the costliest—and deadliest—in U.S.history.

Click “next” to read about the damage tornadoes have caused inthe U.S. in recent years.

What Is a Tornado?

A tornado is a violently rotating column of air that extendsfrom a thunderstorm and comes into contact with the ground,according to the National Oceanic and Atmospheric Administration(NOAA). In an average year, NOAA says about 1,000 tornadoes arereported nationwide.

I.I.I. says tornadoes have caused $97.8 billion in insuredlosses in the U.S. between 1990 and 2009, making these weatherevents second only to hurricanes ($152.4 billion) over this sametime period as the costliest natural disasters.

Tornado intensity is measured by the enhanced Fujita (EF) scale.The scale rates tornadoes on a scale of 0 through 5, based on theamount and type of wind damage. It incorporates 28 different“damage indicators,” based on damage to a wide variety ofstructures ranging from trees to shopping malls.

Source: NOAA

2008-2010

A tornado funnel cloud touchesdown in Orchard, Iowa on June 10, 2008 (AP Photo/LoriMehmen)

From 2008-2010, severe thunderstorms and tornadoes have causedabout $30 billion in insured damages.

The number of tornadoes and the deaths they caused were up in2010, compared with 2009, but below the levels seen in 2008, I.I.I.says. NOAA reports that there were 1,282 tornadoes in 2010, up from1,146 in 2009, and fatalities reached 45, after dropping to 21 in2009.

Tornadoes and thunderstorms caused $13.2 billion in economiclosses and $9.5 billion in insured losses in 2010, according toMunich Re. This was the third consecutive year thunderstorms causedover $9 billion in insured losses. Thunderstorms and tornadoesaccounted for the largest share of insured losses from naturaldisasters in 2010, topping winter storms ($2.6 billion), floods($1.1 billion), earthquakes ($128 million) and tropical cyclones($120 million), according to Munich Re.

Two Red Cross workers walk awayfrom a barn in Mount Pleasant, Wis. that was lifted off itsfoundation by a tornado on Oct. 26, 2010. (AP Photo/CarrieAntlfinger)

2011

Blue tarps cover the roofs homesstill livable along the path of an April 2011 tornado inTuscaloosa, Ala. (AP Photo/Dave Martin)

The year 2011 saw the two costliest tornado events as far asinsured losses, as well as the deadliest tornado since modernrecord-keeping began in 1950.

According to the National Oceanic and Atmospheric Administration(NOAA) there were 1,691 tornadoes in 2011, including 758 tornadoesin April, the highest monthly toll on record.

Storms that spawned the tornadoes in Tuscaloosa, Alabama inApril accounted for $7.5 billion in insured losses, good for the10th costliest natural-catastrophe event, according to ISO. Thestorm system that caused the May 2011 tornado in Joplin, Missouricaused $7 billion in insured damages, and was only recently bouncedfrom the top-10 list by Superstorm Sandy. The Joplin tornado caused158 deaths, making it the deadliest tornado since modernrecord-keeping began, according to NOAA.

Overall, insured losses from tornadoes/thunderstorms were over$25 billion in 2011, more than double the previous record, I.I.I.says.

A scene from Joplin, Mo. after adeadly tornado struck in May 2011 (Credit: Bryant Rousseau,PC360)

2012-2013

A photo taken May 24, 2012 showsa tornado seconds after lifting off the ground near Cornlea, Neb.(AP Photo/Nick Brichacek)

Severe U.S. thunderstorms, including tornado events, cost $14.9billion in insured losses and $27.7 billion in economic losses in2012, according to Munich Re.

This year, I.I.I. says the “devastating tornadoes which hitOklahoma this May bring to the mind a powerful string of tornadoesthat hit Oklahoma, Kansas, Texas, Georgia and 13 other states in1999.”

Those tornadoes, according to ISO, resulted in $1.5 billion ininsured losses ($2.0 billion in 2012 dollars) in all the affectedstates, with nearly $1.0 billion ($1.4 billion in 2012 dollars) inOklahoma alone. Moore, Okla. was one area heavily impacted by the1999 tornadoes.

Scenes from Moore, Okla. in onMay 4, 1999 after a tornado flattened many houses. The powerfultornado in suburban Oklahoma City Monday, May 20, 2013, looselyfollowed the same path as the 1999 twister. (AP Photo/J. PatCarter, File)

Editor's Note:Thanks to I.I.I. for compiling the above information.

Corrected toreflect that the storm systems that spawned the Tuscaloosa andJoplin tornadoes caused the $7.5 billion and $7 billion in insureddamages, rather than the tornadoes by themselves.